How PROC SQL helps you see missing values and other data attributes

The first database (master) is my actual database which has rows indicating time periods during which measurements were taken for each subject; I want to keep ALL of those rows. I want to add in data from the second database (additional) based on whether "additional" has values that correspond to the time periods in each of the rows in "master". If there are no measurements in “additional” that correspond to the specified time periods, I would like for those rows to be retained as missing values, instead of dropped. For instance, for example Subject #001, I want to merge data from “additional” into the “master” database to produce the “want” database below:

Master:

StudyID

StartDate_C

EndDate1_C

Date_12mopost

001

01/04/2012

07/10/2012

01/04/2013

001

03/07/2013

06/18/2013

03/07/2014

001

06/25/2013

01/01/2015

06/24/2014

Want (desired combined database):

StudyID

StartDate_C

EndDate1_C

Date_12mopost

full_lab_Date

001

01/04/2012

07/10/2012

01/04/2013

.

001

03/07/2013

06/18/2013

03/07/2014

.

001

06/25/2013

01/01/2015

06/24/2014

07/31/2013

001

06/25/2013

01/01/2015

06/24/2014

11/22/2013

I used left join (code below), but it looks like this code is still causing rows without matches in “additional” to be dropped:

procsql;

create table want as

select c.*, v.*

from WORK.master AS c left join WORK.additional AS v

on c.StudyID=v.StudyID_copy

where c.StartDate_C <= v.full_lab_date <= c.DATE_12MOPOST ;

;

quit;

want (using the code above, which produces something different than what I want):

StudyID

StartDate_C

EndDate1_C

Date_12mopost

full_lab_DATE

001

06/25/2013

01/01/2015

06/24/2014

07/31/2013

001

06/25/2013

01/01/2015

06/24/2014

11/22/2013

Is there a modification I can make to my code in order to get the desired outcome?